Glaucoma is a disease in which the optic nerve is damaged, leading to progressive, irreversible loss of vision. It is typically associated with increased pressure of the fluid (i.e., aqueous humor) in the eye. Untreated glaucoma leads to permanent damage of the optic nerve and resultant visual field loss, which can progress to blindness. Once lost, this damaged visual field cannot be recovered. Glaucoma is the second leading cause of blindness in the world, affecting 1 in 200 people under the age of fifty, and 1 in 10 over the age of eighty for a total of approximately 70 million people worldwide.
In conditions of glaucoma, the pressure of the aqueous humor in the eye (anterior chamber) increases and this resultant increase of pressure can cause damage to the vascular system at the back of the eye and especially to the optic nerve. The treatment of glaucoma and other diseases that lead to elevated pressure in the anterior chamber involves relieving pressure within the anterior chamber to a normal level.
The importance of lowering intraocular pressure (IOP) in delaying glaucomatous progression has been well documented. When drug therapy fails, or is not tolerated, surgical intervention is warranted. Surgical filtration methods for lowering intraocular pressure by creating a fluid drainage pathway between the anterior chamber and an area of lower pressure have been described. Intraocular shunts can be positioned in the eye to drain fluid from the anterior chamber to locations such as the sub-Tenon's space, the subconjunctival space, the episcleral vein, the suprachoroidal space, Schlemm's canal, and the intrascleral space.
Methods of implanting intraocular shunts are known in the art. Shunts may be implanted using an ab externo approach (entering through the conjunctiva and inwards through the sclera) or an ab interno approach (entering through the cornea, across the anterior chamber, through the trabecular meshwork and sclera).
Positioning of an intraocular shunt to drain fluid into the intrascleral space is promising because it avoids contact with the conjunctiva and the suprachoroidal space. Avoiding contact with the conjunctiva and choroid is important because it reduces irritation, inflammation and tissue reaction, which can lead to fibrosis and reduce the outflow potential of the subconjunctival and suprachoroidal space. The conjunctiva itself plays a critical role in glaucoma filtration surgery. A less irritated and healthy conjunctiva allows drainage channels to form and less opportunity for inflammation and scar tissue formation. Intrascleral shunt placement safeguards the integrity of the conjunctiva and choroid, but may provide only limited outflow pathways that may affect the long term IOP lowering efficacy.